[3.2] Adjust model indexes (#587)

tests/typecheck/models/test_indexes.yml

@@ -0,0 +1,10 @@
+-   case: model_index
+    main: |
+        from django.db import models
+        from django.db.models.functions import Lower
+        models.Index(fields=["foo"])
+        models.Index("foo", models.F("bar"), Lower("baz"), name="test")
+        models.Index("foo", name="test", opclasses=["bar"])
+        models.Index("foo", name="test", condition=models.Q(foo=1))
+        models.Index("foo", name="test", include=["bar"])
+